Sense electrode design

ABSTRACT

A touch sensitive device includes a plurality of sense electrodes arranged in a pattern to receive charge from drive electrodes. The pattern of sense electrodes has extreme portions having worst case charge transfer times, wherein the worst case charge transfer time at multiple extreme portions is substantially equal.

RELATED APPLICATIONS

This non-provisional application is a continuation under 35 U.S.C. § 120of U.S. application Ser. No. 16/277,636 filed Feb. 15, 2019, nowpending, which is a continuation of U.S. application Ser. No. 15/915,726filed Mar. 8, 2018, now U.S. Pat. No. 10,228,808, which is acontinuation of U.S. application Ser. No. 12/605,779 filed Oct. 26,2009, now U.S. Pat. No. 9,916,045, entitled “Sense Electrode Design,”each of which is incorporated herein by reference.

BACKGROUND

Touchscreen displays are able to detect a touch such as by a finger orstylus within an active or display area. Use of a touchscreen as part ofa display enables a user to interact with an electronic application bytouching the touchscreen. The display may present images to the user.Such images may include user interface constructs such as differentbuttons, images, or other regions that can be selected, manipulated, oractuated by touch. Touchscreens can therefore provide an effective userinterface for cell phones, GPS devices, personal digital assistants(PDAs), computers, ATM machines, appliances and other devices.

Touchscreens use various technologies to sense touch from a finger orstylus, such as resistive, capacitive, infrared, and acoustic sensors.Capacitive touchscreens often use one or more layers of transverseelectrodes, drive electrodes and sense electrodes. In one type ofcapacitive sensor based touchscreen, a touch changes a capacitance at anode in an array of electrodes overlaying the display device. A node istypically thought of as the area where a drive electrode and a receiveelectrode overlap or otherwise run adjacent.

Transparent electrodes such as indium tin oxide (ITO) or transparentconductive polymers may be used to form the electrodes. Some layouts ofelectrodes utilize a flooded type pattern of drive electrodes to shieldthe sense electrodes from electric field interference from an underlyingdisplay such as a liquid crystal display (LCD). The flooded type patternmay use solid fill drive electrode patterns formed in a layer betweenthe sense electrodes and display.

In some prior touchscreen devices, the layer of electrodes closest tothe display, are the drive electrodes, and run in a first direction. Thesense electrodes include spines that run transverse to the driveelectrodes, and may also include crossbars that run in the samedirection as the drive electrodes. In such prior devices, the resistanceto connection lines from portions of the crossbar electrode farthestfrom connection lines on the touchscreen is greater than the resistanceto connection lines from portions of the crossbars closer to theconnection lines. The electronics may contain sense circuitry having asense capacitor. The sense circuitry operate to accommodate a worst casecharge transfer time, having resistive and capacitive components, toallow sufficient charge to transfer from the drive electrodes throughthe sense electrodes to the sense capacitor. Long charge transfer timescould significantly slow down the operation of the touchscreen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic representation of an electrode layout for a touchsensitive device according to an example embodiment.

FIG. 1B is a schematic representation of an alternative electrode layoutfor a touch sensitive device according to an example embodiment.

FIG. 2 is a schematic representation of an alternative sense electrodelayout according to an example embodiment.

FIG. 3 is a schematic representation of a further alternative senseelectrode layout according to an example embodiment.

FIG. 4 is a schematic representation of a further alternative senseelectrode layout for a touch sensitive device according to an exampleembodiment.

DETAILED DESCRIPTION

FIGS. 1A and 1B are schematic representations of an electrode layout foran example touch sensitive device 100 such as a touchscreen. In oneembodiment, a plurality of longitudinal drive electrodes 110, 112, 114,116, 118, and 120 are formed in one layer. The drive electrodes may alsobe referred to as X electrodes. In the example shown, the driveelectrodes are bar shaped, and completely filled in to help create ashield from electric field interference from an underlying displaydevice, such as a liquid crystal display (LCD). This type of driveelectrode layout may be referred to as a flooded X pattern. The distancebetween the drive electrodes may be minimized in one embodiment toprovide better shielding. The dimensions shown in the drawings may notbe to scale and are not meant to be an accurate representation of thedimensions that may be used in various embodiments, but rather may beexaggerated to more clearly illustrate the concepts described herein.

In further embodiments, the drive electrodes 110, 112, 114, 116, 118,and 120 may be other than rectangular in shape, and may have more of azig-zag pattern to minimize their visibility.

The drive electrodes 110, 112, 114, 116, 118, and 120 may be coupled viadrive lines 121, 122, 123, 124, 125, and 126 to electronics 130 to drivethe drive electrodes during operation of the touch sensitive device 100.In addition to the drive electrodes, one or more sense electrodes 135,137 may run transverse to the drive electrodes. In one embodiment, thesense electrodes 135, 137 may be formed of a conductive transparentmaterial such as indium tin oxide (ITO) or transparent conductivepolymers. Such materials, which while conductive, have a resistance. Theresistance of electrodes made of such materials may change depending onthe width of the electrode.

The sense electrodes 135, 137 may be coupled to electronics 130 viaconnection lines 140 and 142 respectively. In one embodiment, theconnection lines 140 and 142 may be highly conductive and formed ofmetal. The sense electrodes are single connected in one embodiment, inthat only one end of the sense electrodes is coupled to the electronics130. In one embodiment, sense electrodes 135 and 137 include a spinethat runs transverse to the drive electrodes, and may also includecrossbars transverse to the spine of sense electrode 135 and havingdifferent widths as indicated at 150, 152, 154, 156, 158, and 160. Thecrossbars run in the same direction as corresponding drive electrodesand are positioned over the respective drive electrodes 110, 112, 114,116, 118, and 120.

In one embodiment, the crossbars extend from both sides of the spines,and have tips indicated on one end of the crossbars at 161, 162, 163,164, 165, and 166 that are the furthest distance from the spine 135. Theother ends of the crossbars may be the same distance from the spine 135in various embodiments. The width of the crossbars in one embodimentincreases with distance from the end of the spines coupled to theconnection lines 140, 142. The increase in width decreases theresistance of the crossbars while increasing their capacitance to thedrive electrodes. In one embodiment, the increase in width keeps thecharge transfer time of each crossbar at or under a desired threshold.The charge transfer time is the time it takes to transfer sufficientcharge from the drive electrodes through the sense electrodes to thesense capacitor. In a further embodiment, the charge transfer time ofeach crossbar is substantially equal, taking into account processtolerances.

Thus, it can be observed that the width of crossbar 150 is fairlynarrow. The width increases with successive crossbars 152-160 such thatthe widest crossbar 160 is furthest from the connection line 140. In oneexample embodiment, the width of the spine of sense electrode 135 may beapproximately 1 mm, and the width of the crossbars may progress from 0.2mm to 0.5 mm or wider, including wider than the spine in someembodiments. Note that spine 137 has corresponding crossbars, as wouldadditional spines as represented by the dots. The crossbars fromadjacent spines may run adjacent to each other in further embodiments.In one embodiment, the crossbars extend about 75 percent of the distancebetween the spines, and thus run adjacent together for about 50 percentof their length as shown. The amount of adjacent run may vary in furtherembodiments. The spines may be narrower or wider than 1 mm in variousembodiments consistent with desired charge transfer time and visibilityconstraints.

In one embodiment, the widths of the crossbars may be determined bystarting with the worst case charge transfer time. In FIGS. 1A and 1B,the worst case charge transfer time would be the longest path from tip166 of crossbar 160, along the spine of sense electrode 135 toconnection line 140. After determining the width of crossbar 160 inaccordance with a desired charge transfer time, the remaining crossbarwidths are chosen to obtain charge transfer times equal to or less thanthe desired charge transfer time. The charge transfer time is generallya function of a resistance and a capacitance, where the resistance isthe resistance from crossbar tip to the connection line of the senseelectrode, and the capacitance is the capacitance between the driveelectrodes and the sense electrode. The capacitance is affected by touchproximate the intersection of a sense electrode and a drive electrode.The worst case charge transfer time, T, may be calculated and used as athreshold or design parameter for ensuring that the charge transfer timeat the tips of each crossbar is less than the worst case T, or equal toit. This results in the illustrated pattern of crossbar widthsincreasing with increased distance from the connection line.

Since some crossbars may be narrower, the capacitance may be reducedover the length of the sense electrodes. Sense electrodes may beincreased in width to reduce the worst case charge transfer time. Theuse of wider crossbars for selected crossbars allows a reduction in theworst case charge transfer time. Narrower crossbars for selectedcrossbars reduces the capacitive coupling between the sense electrodesand the drive electrodes and hence allows a reduction in overallthickness of sensing portions of touch sensitive devices. This reductionin sense electrode layer thickness may result in a reduced overall touchsensitive device thickness, and may further reduce drive electrode tosense electrode separation.

In some embodiments, the worst case charge transfer time may be reducedby making some of the crossbars wider, while others already having ashorter charge transfer time may be made narrower.

In one embodiment, a sense electrode design may be optimized by making aworst case charge transfer time equal at all extremes of the electrodedesign. Such designs may or may not include crossbars, and the extremesof the design may or may not have electrode structures with equalwidths. The charge transfer times of such sense electrodes should besubstantially equal such that the charge transfer time does notadversely impact operation of a touch sensitive device. In oneembodiment, the extremes of the design may correspond to portions of theelectrode design that are furthest from a connection line that has arelatively higher conductivity than that of the electrode. In furtherembodiments, the extremes of the electrode design may additionallycorrespond to portions of the electrode design that have smaller widthsthan other portions of the design, and may not directly correspond toportions of the design that are furthest from higher conductivityconnection lines. In some embodiments, there may be a mixture of suchextremes, including remote portions and narrow portions of theelectrodes. In one embodiment, the width of such portions may bemodified to ensure that the sense electrodes have a charge transfer timethat is equal to or better than a desired worst case charge transfertime.

The layout of FIG. 1B shows sense electrodes with varying crossbarwidths as described above. In FIG. 1B, adjacent sense electrodes arearranged to be coupled to connection lines on alternate opposite ends.This results in the width of electrodes progressing along the spinesfrom alternate opposite ends. The adjacent crossbars from adjacentspines are arranged such that the widest crossbars runs adjacent to thenarrowest crossbars, while crossbars of medium width run adjacent toeach other. Thus the combined width of the adjacent crossbars may befairly equal in some embodiments over the length of the spines.

FIG. 2 is a schematic representation of an alternative sense electrodelayout 200 according to an example embodiment. Layout 200 shows onesense electrode 210 having a spine 215 with multiple transversecrossbars 220, 221, 222, 223, 224, 225, and 226. Sense electrode 210 inone embodiment is double connected, meaning that both ends of the senseelectrode 210 are coupled to connection lines as indicated by connectionlines 230 and 235. For each electrode, the corresponding connectionlines 230 and 235 are coupled together for coupling to a controller toindividually sense signals from the electrodes. Since sense electrode210 is connected on both ends, the crossbar being furthest from aconnection line is actually the middle crossbar 223. Crossbar 223 wouldbe the crossbar exhibiting the worst case charge transfer time, but asshown, it has been widened to obtain a desired charge transfer time. Thecrossbars continue to decrease in width in both directions from crossbar223 toward respective connection lines 230 and 235.

In one embodiment, with an odd number of crossbars, crossbars 222 and224 may be equal in width, crossbars 221 and 225 may be equal in width,and crossbars 220 and 226 may also be equal in width. With an evennumber of crossbars, there may be two middle crossbars with equal width,rather than one. Both may be the same distance from a connection line,and thus, the worst case charge transfer time from their tips to theconnection lines may be the same. The rest of the crossbars may besuccessively narrower, as there is no need to make them as wide as thewidest crossbar. In fact, in one embodiment, it is desired that thecharge transfer time from the tip of each crossbar to the nearestconnection line be equal, meaning that the width is decreased as thedistance to the nearest connection line decreases. Additional senseelectrodes that have the varying width crossbar arrangement may beprovided as indicated by the additional sense electrode with crossbarsrunning adjacent crossbars 220, 221, 222, 223, 224, 225, and 226, anddots indicating a repeating pattern of sense electrodes. It isunderstood that the dimensions of FIG. 2, as well as the other drawings,may not be to scale and are not meant to be an accurate representationof the dimensions that may be used in various embodiments, but rather,the dimensions may be exaggerated to more clearly illustrate theconcepts described herein.

FIG. 3 is a schematic representation of a further alternative senseelectrode layout 300 according to an example embodiment. Layout 300includes a sense electrode 310 having different widths 312, 314, 316,and 318 along its spine. Several transverse crossbars 320, 322, 324, and326 are shown coupled to the sense electrode 310. As shown, the width ofthe spine increases with increasing distance from a single connectedconnection line 330. With each increase of spine width in oneembodiment, a crossbar is coupled to the sense electrode. The crossbarsmay be connected at other points on the sense electrode where the senseelectrode does not transition in width. In further embodiments, thewidth of the sense electrode may continuously vary, or may vary in astepwise manner, with multiple crossbars coupled to each section ofconstant width. Various embodiments may include adjacent senseelectrodes arranged to be coupled to connection lines on alternateopposite ends as illustrated in FIG. 1B.

The crossbars 320, 322, 324 and 326 are also shown as varying in theirwidth. As previously described, the worst case charge transfer time froma tip of the crossbar farthest from the connection line 330 may be used.In this case, that would be crossbar 326. The charge transfer time againis the total charge transfer time from the tip of the crossbar 326 tothe connection line 330. In this case, the charge transfer time may bereduced by the fact that the spine is increasing in width. Thus, thewidth of crossbar 326 may not be as wide as in previous embodiments tomeet a desired worst case charge transfer time. The same reduction inwidth for succeeding crossbars closer to connection line 330 may also beobtained. As with previous electrode patterns, additional spines withcrossbars may be provided in various patterns to obtain a pattern havinga desired area.

FIG. 4 is a schematic representation of a further alternative senseelectrode layout 400 for a touch screen. Six spines 410, 412, 414, 416,418 and 420 are shown and representative of sense electrodes for anentire touchscreen in one embodiment. Each of the spines may be doubleconnected such that both ends may be coupled to sense circuitry. Similarto FIG. 2, each spine has multiple transverse crossbars. Twenty ninecrossbars per spine are illustrated. Since the spines are connected onboth ends, the crossbar being furthest from a low resistance connection(not shown) to the sense circuitry is actually the middle crossbar 425,which is the 15th crossbar from either end of the spines. Crossbar 425is thus the crossbar exhibiting the worst case charge transfer timeuntil it is widened as shown to obtain a desired charge transfer time.The crossbars continue to decrease in width in both directions fromcrossbar 425 toward respective connections to sense circuitry.

The invention claimed is:
 1. A touch sensitive device comprising: alayer of longitudinal adjacent drive electrodes separated from eachother by a gap, the layer of longitudinal adjacent drive electrodes tobe positioned above a display; and a layer of sense electrodes formed inthe shape of spines extending transversely to the drive electrodes, thespines each having first and second ends, both of which are adapted tocouple to sense circuitry, and each spine having coextensive-pairs ofcrossbars of substantially equal width extending from opposite sides ofthe spine in the same direction as the drive electrodes such thatportions of crossbars that run in the same direction as the driveelectrodes have different widths than portions of other crossbars thatrun in the same direction as the drive electrodes; wherein the crossbarpairs of each spine are arranged with increasing width from the firstand second ends to couple to the sense circuitry.
 2. The touch sensitivedevice of claim 1 wherein the sense electrodes are formed of atransparent conductive material.
 3. The touch sensitive device of claim1 wherein each crossbar on a spine has at least one tip that is furthestfrom the spine, and wherein a worst case charge transfer time from thetips to one of the two ends of the spine to couple to sense circuitrydoes not exceed a predetermined threshold.
 4. The touch sensitive deviceof claim 3 wherein the predetermined threshold is determined to ensure adesired charge transfer time is not exceeded.
 5. The touch sensitivedevice of claim 3 wherein the worst case charge transfer time from eachtip is substantially equal.
 6. A method comprising: forming a layer oflongitudinal adjacent drive electrodes separated from each other by agap, the layer of longitudinal adjacent drive electrodes to bepositioned above a display; and forming a layer of sense electrodes inthe shape of spines extending transversely to the drive electrodes, thespines each having first and second ends, both of which are adapted tocouple to sense circuitry, and each spine having coextensive pairs ofcrossbars of substantially equal width extending from opposite sides ofthe spine in the same direction as the drive electrodes such thatportions of crossbars that run in the same direction as the driveelectrodes have different widths than portions of other crossbars thatrun in the same direction as the drive electrodes; wherein the crossbarpairs of each spine are arranged with increasing width from the firstand second ends to couple to the sense circuitry.
 7. The method of claim6 wherein the sense electrodes are formed of a transparent conductivematerial.
 8. The method of claim 6 wherein each crossbar on a spine hasat least one tip that is furthest from the spine, and wherein a worstcase charge transfer time from the tips to one of the two ends of thespine to couple to sense circuitry does not exceed a predeterminedthreshold.
 9. The method of claim 8 wherein the predetermined thresholdis determined to ensure a desired charge transfer time is not exceeded.10. The method of claim 8 wherein the worst case charge transfer timefrom each tip is substantially equal.